package com.ctsi.commons.util.id;

public class IdGen {
	private final long workerId;
	private final long datacenterId;
	private long sequence = 0L;
	private final long twepoch = 1288834974657L; // Thu, 04 Nov 2010 01:42:54 GMT
	private final long workerIdBits = 5L; // 节点ID长度
	private final long datacenterIdBits = 5L; // 数据中心ID长度
	private final long maxWorkerId = -1L ^ (-1L << workerIdBits); // 最大支持机器节点数0~31，一共32个
	private final long maxDatacenterId = -1L ^ (-1L << datacenterIdBits); // 最大支持数据中心节点数0~31，一共32个
	private final long sequenceBits = 12L; // 序列号12位
	private final long workerIdShift = sequenceBits; // 机器节点左移12位
	private final long datacenterIdShift = sequenceBits + workerIdBits; // 数据中心节点左移17位
	private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits; // 时间毫秒数左移22位
	private final long sequenceMask = -1L ^ (-1L << sequenceBits);
	private long lastTimestamp = -1L;

	private static class IdGenHolder {
		private static final IdGen instance = new IdGen();
	}

	public static IdGen get() {
		return IdGenHolder.instance;
	}

	public IdGen() {
		this(0L, 0L);
	}

	public IdGen(long workerId, long datacenterId) {
		if (workerId > maxWorkerId || workerId < 0) {
			throw new IllegalArgumentException(String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
		}
		if (datacenterId > maxDatacenterId || datacenterId < 0) {
			throw new IllegalArgumentException(String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
		}
		this.workerId = workerId;
		this.datacenterId = datacenterId;
	}

	public long nextId() {
		long timestamp = timeGen();
		synchronized (this) {
			if (timestamp < lastTimestamp) {
				throw new RuntimeException(String.format("Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
			}
			if (lastTimestamp == timestamp) {
				sequence = (sequence + 1) & sequenceMask;
				if (sequence == 0) {
					timestamp = tilNextMillis(lastTimestamp);
				}
			} else {
				sequence = 0L;
			}
			lastTimestamp = timestamp;
			return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift) | (workerId << workerIdShift) | sequence;

		}
	}

	private long tilNextMillis(long lastTimestamp) {
		long timestamp = timeGen();
		while (timestamp <= lastTimestamp) {
			timestamp = timeGen();
		}
		return timestamp;
	}

	private long timeGen() {
		return System.currentTimeMillis();
	}
}
